He also sent another mare, Keep It Cool, to I Am Invincible – a mating that produced Kool Vinnie, also owned by Tonkin and Hill.

Kool Vinnie kept the pot boiling while Invincible Gem was out spelling, putting back-to-back wins together at Taree in June.

“Theo and his father always bred a few thoroughbreds and he took a couple of his mares to I Am Invincible, but he sadly passed away just after the foals were born,” Tonkin said.

“What’s so amazing is that there is no black type back in Invincible Gem’s dam side for five generations. She’s just a bush-bred horse – something that just developed out of the blue.

“We decided on New Year’s Day last year to keep the racehorses in the family – Charles said at the time that he thought they’d be all right – and we’ve been halves ever since.

“That’s how it all came about – this is the first time in my life I’ve ever been involved in racehorses, or racing.”

Invincible Gem, trained at Newcastle by Kris Lees, has won five times from just 10 starts and is conservatively valued at just under $1 million.

When – not if – she wins at Group 1 level, her value will skyrocket.

Last preparation she made a cakewalk of the 1600m Group 3 Spring Stakes at Royal Randwick, beating the boys by nearly four lengths.

She had previously won at Canterbury, Warwick Farm and Rosehill.

Her prize money tally currently hovers around the $500,000 mark and is set to rise even further in the coming weeks.

“When this little journey began we were just hoping that we might have a horse that could win at Newcastle, some day. The Provincial Championships was the original plan, but winning that black type race at Randwick buggered that,” Tonkin smiled.

“Winning that race at Randwick was a bit emotional, too. Theo bred her and he’s bred horses for generations and now having a horse that has won Group races in Sydney is something that we never thought would happen.

“Kris says she is just getting better and better and better – but he still calls her a plain-looking filly that hasn’t got a lot of breeding.”

Lees said he is forever amazed at how Invincible Gem has improved.

“It’s amazing. She’s certainly surprised me in the way she’s winning and where she’s come from,” he said.

Tonkin and Hill, a couple of self-confessed bushies humbled by such an extraordinary run of racetrack success, have quickly become well-known faces on city tracks.